P0300 on a BMW: Causes, Fixes & Repair Cost

🟠 Moderate severity · drivable

If the check engine light is flashing, stop driving — a severe misfire can damage the catalytic converter. A steady light is usually safe for a short drive to a shop.

What P0300 means on a BMW

On a BMW, P0300 means the engine computer sees misfires jumping between cylinders instead of on one fixed cylinder. A misfire means a cylinder is not burning its fuel properly, which wastes gas and can damage the catalytic converter if left alone.

Is P0300 common on BMWs?

P0300 is common on BMW inline-6 engines, especially the turbocharged N54 and N55 in the 335i and 535i, where ignition coils fail frequently. Spark plugs and fuel injectors are other common causes on these engines. Vacuum leaks from aged hoses also trigger random misfires.

Commonly reported on: 3 Series, 5 Series, X3, X5.

Symptoms

Check engine light on (flashing if severe)
Rough idle or shaking engine
Loss of power or hesitation
Poor fuel economy

Common causes

most common: Failing ignition coils
common: Worn spark plugs
common: Clogged or leaking fuel injectors
less common: Vacuum leak
less common: Low compression from engine wear

How to fix it

Fix	DIY?	Typical cost
Replace failing ignition coils	Yes	$150–400
Replace worn spark plugs	Yes	$100–250
Replace faulty fuel injectors	Mechanic	$400–1200
Find and repair vacuum leaks	Yes	$10–100